From: "Frank Q" 
To: "Vladimir Galogaza" ,
        "ATM shore" 
Reply-To: "Frank Q" 



----- Original Message -----
From: "Vladimir Galogaza" 
To: "ATM shore" 
Sent: Thursday, March 06, 2003 4:03 PM Subject: Re: ATM Diffraction due to
secondary sizing.


>
>
> >One way I know of for eliminating rings is through apodization, but
> >then this just increases the size of the central disk - you have just
> >as much resolution as before - no more, no less.
>
> I seriously doubt this " no more no less" statement.
>
> Resolution problem due to diffraction on aperture boils down
> to the Airy disk size. Increasing the central disk size equals loss of
> resolution, fringes or not. This is so because of how resolution is
defined.

But you still have the rings that interfere with the detail in the image in the
vicinity of the the Airy disk. --- Apodization increases the diameter of
the central maximum, and if you choose a suitable profile (eg gaussian),
the central
disk would be insignificant (not detectable with your eyes) just about
where the first ring started. Try experimenting with Fourier transforms of
circular apertures with and without a modulation factor applied across the
surface.

After having written the above paragraph, it is obvious that a more
accurate (versatile ??) definition of "resolution" is required
!!!

BUT - the bottom line is -- If your magnification is high enough that you
have to mentally interpret what the image would look like in the absence of
diffraction, then is that image really worth looking at ?

I would rather lower the magnification, get a better and wider field of
view and enjoy looking through the telescope rather than worry about the
idiosyncracies of different diffraction patterns.

>
> Loss or increase of contrast is just another consequence of diffraction.
> But keeping resolution and decreasing aperture is contradictio in adjecto.
> In usual noncoherent case. Interferometric Aperture synthesis for
resolution
> increase is not what we are talking about on this thread.
>
> Redefining definition of resolution is possible but then we are not
talking
> about the same thing.
>
>
>

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